What does it mean when you are preselected for a credit card?

That's just a term that marketers use. They buy your name and personal information from a credit bureau or from another business, and mail you a notice saying that you can apply for their credit card. You still have to be approved once you apply. There are normally a lot of asterisks, footnotes or "terms and conditions" clauses in small print that you should read. Applying for credit, whether or not you ever use it, can affect your credit rating.